• Authors:
    • Okoth, S. A.
    • Wachira, P. M.
    • Matiru, V. N.
    • Muthuri, C. W.
    • Jefwa, J. M.
    • Nyaga, J.
  • Source: Article
  • Volume: 103
  • Issue: 2
  • Year: 2015
  • Summary: Several interrelated and site-specific agronomic factors ranging from agroecological conditions to systems management practices have been shown to variably affect arbuscular mycorrhizal fungi (AMF) diversity in the soil. Also, there have been various attempts in the past to evaluate the potential of AMF field inoculation but a majority focussed on the use of exotic strains, disregarding the potential of the existing naturally occurring strains. In an attempt to address these problems, our study aimed to develop 'best-bet practice' based on soil fertility amendment practice (SFAP) that encourages occurrence and diversity of AMF in the soil. Control treatment (no application) was compared with three (3) SFAP used singly or in combination with AMF or two other soil nutrients enhancing organisms (Bacillus and Trichoderma) which included the following: (1) Mavuno (macro- and micronutrients and secondary nutrients) fertilizer, (2) calcium ammonium nitrate (CAN) plus triple super phosphate (TSP) and (3) cattle manure. Maize (Zea mays L.) and common bean (Phaseoli vulgaris L.) were planted at on-station and on-farm plots for two consecutive cropping seasons with the experiment replicated in two benchmark sites of Embu and Taita-Taveta Districts. Embu site recorded a lower soil pH and also very low phosphorus levels compared to Taita site. The number of AMF spores per kg of soil was very low, ranging from 30 to 100, at Embu in the first season and application of SFAP resulted in no significant difference. However, in the second season, use of Trichoderma + CAN plus TSP was shown to significantly stimulate AMF species in the soil, with a 250 % increase in species density compared to use of Bacillus + Manure. At Taita, after the first cropping season, significant change in spore density was only recorded from AMF applied singly with a 66.1 % increase in spore density compared to Control treatment. In comparison, after the second cropping season, use of AMF applied singly, AMF + CAN plus TSP and AMF + Manure increased spore density by 135.4, 109.6 and 100 % respectively compared to Control treatment. Use of AMF applied singly increased species density in the soil by 100 and 81.1 % compared to CAN plus TSP and Trichoderma treatments respectively after first season at Taita site: while after the second cropping season, application of AMF + CAN plus TSP, AMF + Manure and AMF + Mavuno increased AMF species density in the soil by 60.3, 51.5 and 55.9 % respectively compared to Control treatment. These findings provide evidence that it is possible to increase the number of AMF spores in the soil through inoculation with native species and also possibly stimulate dormant species through other SFAP treatments.
  • Authors:
    • Rathmann, R.
    • Soria, R.
    • Portugal-Pereira, J.
    • Schaeffer, R.
    • Szklo, A.
  • Source: Article
  • Volume: 81
  • Year: 2015
  • Summary: This study aims to quantify the environmentally sustainable and economically feasible potentials of agricultural and agro-industrial residues to generate electricity via direct combustion in centralised power plants in Brazil. Further, the energy savings and greenhouse gas (GHG) reduction potential of replacing natural gas-based electricity by bioenergy have been assessed. To this end, a methodology has been developed based on an integrated evaluation, incorporating statistical and geographical information system (GIS)-based analysis, and a life-cycle-assessment approach. Results reveal that the environmentally sustainable generation potential is nearly 141 TWh/year, mainly concentrated in the South, Southeast, and Midwest regions of the country. Sugarcane, soybean and maize crop residues are the major feedstocks for available bioenergy. On the other hand, the economic potential is far lower, accounting to 39 TWh/year. The total GHG mitigation is nearly 18 million tonne CO 2e and could reach 64 million tonne CO 2e yearly, if the technical potential is considered. The gap between technical and economic potentials implies that constraints to bioenergy are not related to a lack of resources, but rather associated to economic, logistical, regulatory and political barriers.
  • Authors:
    • Drag, D. W.
    • Siebers, M. H.
    • Ruiz-Vera, U. M.
    • Ort, D. R.
    • Bernacchi, C. J.
  • Source: Primary Research Article
  • Volume: 21
  • Issue: 11
  • Year: 2015
  • Summary: Rising atmospheric CO 2 concentration ([CO 2]) and attendant increases in growing season temperature are expected to be the most important global change factors impacting production agriculture. Although maize is the most highly produced crop worldwide, few studies have evaluated the interactive effects of elevated [CO 2] and temperature on its photosynthetic physiology, agronomic traits or biomass, and seed yield under open field conditions. This study investigates the effects of rising [CO 2] and warmer temperature, independently and in combination, on maize grown in the field throughout a full growing season. Free-air CO 2 enrichment (FACE) technology was used to target atmospheric [CO 2] to 200 mol mol -1 above ambient [CO 2] and infrared heaters to target a plant canopy increase of 3.5°C, with actual season mean heating of ~2.7°C, mimicking conditions predicted by the second half of this century. Photosynthetic gas-exchange parameters, leaf nitrogen and carbon content, leaf water potential components, and developmental measurements were collected throughout the season, and biomass and yield were measured at the end of the growing season. As predicted for a C 4 plant, elevated [CO 2] did not stimulate photosynthesis, biomass, or yield. Canopy warming caused a large shift in aboveground allocation by stimulating season-long vegetative biomass and decreasing reproductive biomass accumulation at both CO 2 concentrations, resulting in decreased harvest index. Warming caused a reduction in photosynthesis due to down-regulation of photosynthetic biochemical parameters and the decrease in the electron transport rate. The reduction in seed yield with warming was driven by reduced photosynthetic capacity and by a shift in aboveground carbon allocation away from reproduction. This field study portends that future warming will reduce yield in maize, and this will not be mitigated by higher atmospheric [CO 2] unless appropriate adaptation traits can be introduced into future cultivars.
  • Authors:
    • Liang, L.
    • Jia, Z.
    • Wang, X.
  • Source: Soil and Tillage Research
  • Volume: 153
  • Year: 2015
  • Summary: Field experiments were conducted in 2008-2010 in the Loess Plateau of China to study the effects of straw incorporation on maize growth and biomass water use efficiency (WUE) under semi-arid condition in dark loessial soil. Low (LS 4.5tha-1), medium (MS 9.0tha-1), and high (HS 13.5 tha-1) levels of straw were incorporated into the surface soil combined with fixed levels of inorganic fertilizers (CK) as control. Straw incorporation compared with CK significantly improved biomass yield at the tasseling-maturity stage of maize and WUE at the jointing-ten leaf collar and the tasseling-grain filling stages. WUEs with LS and MS treatments were significantly lower than that with CK at the ten leaf collar-tasseling stage, although the WUEs with MS and HS treatments were significantly higher in the whole growth period. HS treatment compared with LS treatment significantly increased biomass yield at the ten leaf collar-maturity stage and WUE at the jointing-tasseling stage. Meanwhile, MS and HS treatments compared with LS treatment significantly increased the biomass yield at the late grow period. Straw incorporation significantly improved WUE at the sowing-jointing stage and soil organic carbon relative to CK. Biomass yield at the ten leaf collar stage and WUE in whole growth period with LS treatment were significantly higher compared with CK. WUE at the ten leaf collar-tasseling and the grain filling-maturity stages were significantly higher with HS treatment compared with CK. In the long term, the rational straw incorporation level in improving maize biomass yield and WUE was 9.0tha-1. © 2015 Elsevier B.V..
  • Authors:
    • Wilkens,S.
    • Weimer,P. J.
    • Lauer,J. G.
  • Source: Agronomy Journal
  • Volume: 107
  • Issue: 6
  • Year: 2015
  • Summary: Full-season corn ( Zea mays L.) hybrids take advantage of more of the growing season than shorter-season hybrids often leading to greater grain and biomass yield. Many agronomic experiments aimed at corn stover production have been performed at forage harvest rather than later when stover is normally harvested for biofuel measurements. The objective of this research was to evaluate the influence of hybrid relative maturity (days RM) on stover ethanol production, ruminant digestibility, and biomass composition. Hybrids selected were high-yielding commercial grain hybrids grown throughout Wisconsin and ranged from 85 to 115 d RM in 10 d RM increments during 2009, and in 5 d RM increments during 2010. Hybrids were harvested at physiological maturity or after a killing frost. Overall, stover and theoretical ethanol yields increased as RM increased at a linear rate of 0.211 Mg ha -1 RM -1 and 67.1 L ha -1 RM -1. Stover nutritional and biomass composition improved as RM increased, but yield variability was greater than nutritional and biomass compositional variability. Increasing ethanol yields will likely occur by increasing stover yields rather than by altering stover composition. Therefore, until price premiums for stover composition are made available to farmers for ethanol production, the adoption of full-season or longer maturing hybrids should be implemented for increased stover and ethanol yields.
  • Authors:
    • Siebert, S.
    • Wolf, J.
    • Hoffmann, H.
    • Webber, H.
    • Gang, Z.
    • Ewert, F.
  • Source: Primary Research Article
  • Volume: 21
  • Issue: 11
  • Year: 2015
  • Summary: This study evaluates the impacts of projected climate change on irrigation requirements and yields of six crops (winter wheat, winter barley, rapeseed, grain maize, potato, and sugar beet) in Europe. Furthermore, the uncertainty deriving from consideration of irrigation, CO 2 effects on crop growth and transpiration, and different climate change scenarios in climate change impact assessments is quantified. Net irrigation requirement (NIR) and yields of the six crops were simulated for a baseline (1982-2006) and three SRES scenarios (B1, B2 and A1 B, 2040-2064) under rainfed and irrigated conditions, using a process-based crop model, SIMPLACE . We found that projected climate change decreased NIR of the three winter crops in northern Europe (up to 81 mm), but increased NIR of all the six crops in the Mediterranean regions (up to 182 mm yr -1). Climate change increased yields of the three winter crops and sugar beet in middle and northern regions (up to 36%), but decreased their yields in Mediterranean countries (up to 81%). Consideration of CO 2 effects can alter the direction of change in NIR for irrigated crops in the south and of yields for C3 crops in central and northern Europe. Constraining the model to rainfed conditions for spring crops led to a negative bias in simulating climate change impacts on yields (up to 44%), which was proportional to the irrigation ratio of the simulation unit. Impacts on NIR and yields were generally consistent across the three SRES scenarios for the majority of regions in Europe. We conclude that due to the magnitude of irrigation and CO 2 effects, they should both be considered in the simulation of climate change impacts on crop production and water availability, particularly for crops and regions with a high proportion of irrigated crop area.
  • Authors:
    • Madejon, E.
    • Murillo, J.
    • Soriano, M.
    • Griffith, D.
    • Carmona, I.
    • Gomez-Macpherson, H.
  • Source: Agriculture, Ecosystems & Environment
  • Volume: 213
  • Year: 2015
  • Summary: Conservation agriculture (CA), which is promoted worldwide to conserve soil, water and energy and to reduce production costs, has had limited success in Europe. The objectives of this study were to assess annual crop systems currently managed under CA in southern Spain, identify obstacles to CA adoption, and recommend strategies to overcome those obstacles. We employed the following methods: (i) examination of original government data used to monitor CA; (ii) survey of CA farmers to characterize their practices and perceptions; (iii) agronomic, economic and energy use comparison of minimum tillage (MT) and conventional tillage (CT); and (iv) a stakeholder focus group to identify strategies for improving CA. Farmers selectively implemented some components of CA while disregarding others as a strategy to adapt to local conditions. Although most researchers define CA as a system that combines minimum soil disturbance, maintenance of crop residues, and crop rotation, in practice most farmers and organizations equated CA with direct seeding of cereals without considering residues or crop rotation. Official national statistics did not include all of these CA components either. Examination of government data revealed that only 13% of monitored plots were not tilled consecutively. The most common CA system (50% of farms) was direct seeded wheat rotated with tilled sunflower. This system (classified as MT) and CT were not significantly different with regard to wheat yield, soil quality, net return or energy use in either crop, which was likely due to similar residues management, recurrent soil disturbance in MT, and disuse of moldboards in CT. In wheat, fertilizers represented the largest energy input (68% TEI) in both systems followed by diesel consumption (12% and 19% in MT and CT, respectively). To overcome the most important identified problems in CA, we highlight the need for collaborative research with farmers and other stakeholders to develop appropriate drill technology for spring crops, identify non-cereal crops that are better adapted to CA than sunflower, improve residues management, increase energy efficiency through better fertilizer management, and promote CA among farmer groups excluded by socioeconomic barriers. Finally, international standards to guide data collection and statistical analyses on all components of CA will enable researchers and institutions to compare information and find solutions to common problems.
  • Authors:
    • Chen, D.
    • Weng, B.
    • Zhang, J.
    • Zheng, X.
    • Hu, X.
    • Zhang, Y.
    • Li, S.
    • Ding, H.
  • Source: Nutrient Cycling in Agroecosystems
  • Volume: 103
  • Issue: 3
  • Year: 2015
  • Summary: To investigate the fate of urea nitrogen (N) applied to vegetable fields, three N rates, N0 (0 kg N/ha), N1(225 or 240 kg N/ha) and N2 (450 or 480 kg N/ha) were applied to a rotation system. Nitrogen fertilizer recovery (NFR), N residue in soil, and N losses were measured in situ. Higher N application rates resulted in lower NFR, and increased N residues in soil and losses. The NFR, Chinese cabbage, and eggplant were different in the N1 and N2 groups (P < 0.01). The ratios of N fertilizer residue at 0-60 cm deep ranged from 30.2 to 41.1 % (N1), and 33.1 to 57.7 % (N2). The N loss ratios were only 6.6 % (N1) and 11.9 % (N2), because of the lower precipitation rates and temperatures characteristic of its growing season; meanwhile, N losses were 31.1 and 37.4 % in cayenne pepper, and 24.1 and 29.2 % in eggplants in the N1 and N2 treatments, respectively. The main pathways of N loss were leaching, followed by gaseous losses; these were major pathways of N loss in seasons with lower precipitation rates. NH3 volatilization was correlated with soil temperature (P < 0.01), and N2O emissions were correlated with soil moisture in the N1 treatment and with soil NH4 (+)-N concentration in the N2 treatment (P < 0.01). Denitrification rates were correlated with soil moisture in the N0 and N1 treatments, and with NO3 (-)-N content in the N2 treatment (P < 0.01). Finally, loss due to runoff was correlated with precipitation (P < 0.01).
  • Authors:
    • Soegaard, K.
    • Rasmussen, J.
    • Askegaard, M.
    • Eriksen, J.
  • Source: Agriculture, Ecosystems & Environment
  • Volume: 212
  • Year: 2015
  • Summary: Intensive dairy farming, with grass-arable crop rotations is challenged by low N use efficiency that may have adverse environmental consequences. We investigated nitrate leaching and N fertility effects of grass-clover leys for five years in two organic crop rotations with different grassland proportions (33 and 67%) and five grassland managements in terms of cutting, grazing, fertilization and combinations thereof. In grass-clover, the combination of fertilization and grazing caused excessive leaching (average 60 kg N ha -1) but leaving out either fertilization or full-time grazing substantially reduced leaching losses to on average 23 kg N ha -1. There was no linear relationship between sward age and nitrate leaching. The annual N surplus of the grasslands was only weakly related to nitrate leaching ( R2=0.05, P50 kg N ha -1) with lupin and maize, where especially maize was consistently high in all five years (average 81 kg N ha -1). Great care should be taken during all phases of the dairy crop rotation where grasslands cause considerable build-up of fertility. With due care and the best management practice, nitrate leaching losses may be reduced to low levels.
  • Authors:
    • Pitombo, L.M.
    • Carmo, J.B.
    • Maria, I.C.
    • Andrade, C.A.
  • Source: Scientia Agricola
  • Volume: 72
  • Issue: 2
  • Year: 2015
  • Summary: The large volume of sewage sludge (SS) generated with high carbon (C) and nutrient content suggests that its agricultural use may represent an important alternative to soil carbon sequestration and provides a potential substitute for synthetic fertilizers. However, emissions of CH 4 and N 2O could neutralize benefits with increases in soil C or saving fertilizer production because these gases have a Global Warming Potential (GWP) 25 and 298 times greater than CO 2, respectively. Thus, this study aimed to determine C and N content as well as greenhouse gases (GHG) fluxes from soils historically amended with SS. Sewage sludge was applied between 2001 and 2007, and maize ( Zea mays L.) was sowed in every year between 2001 and 2009. We evaluated three treatments: Control (mineral fertilizer), 1SS (recommended rate) and 2SS (double rate). Carbon stocks (0-40 cm) were 58.8, 72.5 and 83.1 Mg ha -1 in the Control, 1SS and 2SS, respectively, whereas N stocks after two years without SS treatment were 4.8, 5.8, and 6.8 Mg ha -1, respectively. Soil CO 2 flux was highly responsive to soil temperature in SS treatments, and soil water content greatly impacted gas flux in the Control. Soil N 2O flux increased under the residual effects of SS, but in 1SS, the flux was similar to that found in moist tropical forests. Soil remained as a CH 4 sink. Large stores of carbon following historical SS application indicate that its use could be used as a method for carbon sequestration, even under tropical conditions.